Method of preparing fibrous copper oxide catalyst

ABSTRACT

A FIBROUS COPPER OXIDE CATALYST FOR RENDERING CARBON MONOXIDE AND RESIDUAL HYDROCARBONS CONTAINED IN THE EXHAUST GAS OF INTERNAL COMBUSTION ENGINES HARMLESS IS MANUFACTURED BY THE STEPS OF PREPARING A WEB OR THE LIKE MADE OF A FINE WIRE OF AN IRON BASE HEAT RESISTANT ALLOY CONTAINING NICKEL AND/OR CHROMIUM, APPLYING A MIXTURE CONSISTING OF COPPER OXIDE, METAL HALIDE AND CARBONACEOUS SUBSTANCE UPON THE SAID WEB TO FORM A LAYER OF THE MIXTURE HAVING A UNIFORM THICKNESS, HEATING THE RESULTING ASSEMBLY IN NON-OXIDIZING ATMOSPHERE AT A TEMPERATURE OF ABOUT 750*C. TO FORM FIBROUS COPPER OR FIBROUS COPPER CONTAINING A SMALL QUANTITY OF ANOTHER METAL, THE FIBROUS COPPER BEING FIRMLY BONDED TO THE SAID WEB, AND OXIDIZING THE RESULTANT COMPOSITE BODY TO FORM A FIBROUS COPPER OXIDE OR AN OXIDE OF A FIBROUS COPPER BASE ALLOY.

United States Patent Ofice 3,772,214 Patented Nov. 13, 1973 US. Cl. 252-447 11 Claims ABSTRACT OF THE DISCLOSURE A fibrous copper oxide catalyst for rendering carbon monoxide and residual hydrocarbons contained in the exhaust gas of internal combustion engines harmless is manufactured by the steps of preparing a web or the like made of a fine wire of an iron base heat resistant alloy containing nickel and/or chromium, applying a mixture consisting of copper oxide, metal halide and carbonaceous substance upon the said web to form a layer of the mixture having a uniform thickness, heating the resulting assembly in non-oxidizing atmosphere at a temperature of about 750 C. to form fibrous copper or fibrous copper containing a small quantity of another metal, the fibrous copper being firmly bonded to the said web, and oxidizing the resultant composite body to form'a fibrous copper oxide" or an oxide of a fibrous copper base alloy.

This invention relates to a method of manufacturing a fibrous copper oxide catalyst which can efficiently remove harmful compounds such as carbon monoxide (CO) and residual hydrocarbons (HC) contained in the exhaust gas from internal combustion engines of motor cars and the like.

-With recent trend of motorization, the problem of adverse effects of such harmful compounds upon human bodies have become a serious social problem, so that development of an efficient device capable of solving this problem has been desired for many years.

As CO and HC contained in the exhaust gas are formed by the incomplete combustion of the fuel in the internal combustion engine, these gases can be eliminated by the complete combustion of the fuel or by the after burning in the exhaust system.

Although these objects can be attained by increasing the ratio of the air to the fuel, or by using improved spark plugs which enhance complete combustion or by installing air after burners, increase in the ratio of the air to the fuel has a tendency of increasing the quantity of nitrogen oxides (NO whereas improved spark plugs and eificient after burners are not yet available.

By improving only. the design of the internal combustion engine, it is possible to limit the quantities of these harmful gases within the upper limits of the current regulation (according to the regulation of August 1970, the maximum permissible limit of CO is 4.5%). But it would be impossible to pass a stricter regulation which is expected to be enforced in the year of 1973, unless both the mechanical design of the engine and chemical treatment of the exhaust gas are improved further.

Most reliable chemical treatment involves the so called catalytic burning method wherein transition elements (belonging to sub group B) are most frequently used.

Although Platinum (Pt) and Palladium (Pd) are most active catalysts, they are not only expensive but also subject to deteriorated catalytic activities, so that they are not satisfactory for use in motor cars. Cobalt oxides, iron oxides, manganese oxides, copper oxides or chromium oxides or mixture thereof have generally been used, singly or in combination, as the oxidizing catalyst for treating the exhaust gas of motor cars. These oxide catalysts are constructed in the composite form of thin layers deposited from aqueous solutions on such carriers as alumina (A10 silica (SiO or the like which are in the form of, for example, small globular or cylindrical pellets.

These prior art oxide catalysts, can not completely render the motor car exhaust gas harmless.

It is therefore an object of this inventionv to provide more efficient oxide catalyst for use in treating motor car exhaust gas.

Another object of this invention is to provide improved oxide catalyst for treating motor car exhaust gas which does not deform, fall off or melt while it can treat the exhaust gas at higher space velocities with extremely small pressure loss.

Generally speaking, according to this invention, the catalyst for purifying the exhaust gas of internal combustion engines is prepared by the steps of preparing web or the like made of a fine Wire of an iron base heat resistant alloy containing nickel and/ or chromium, applyin a mixture substance upon the web to form a layer of the mixture having a uniform thickness, heating the resulting assembly in a nonoxidizing atmosphere at a temperature of about 750 C. to form fibrous copper or fibrous copper containing a small quantity of another metal, the fibrous, copper being firmly bonded to the Web, and oxidizing the resulting composite body to form a fibrous copper oxide or an oxide of a fibrous copper base alloy.

Different from prior art catalysts on the market, the catalyst manufactured by the method of this invention is characterized by its fine fibrous structure.

It has already been proposed to manufacture copper fibers at a high yield by mixing together a copper oxide, a metal halide, and a carbonaceous substance such as graphite. It was found that the fibrous metal copper manufactured by this method and having a diameter of 2 to 3 microns and a length of 300 to 500 microns has an extremely high chemical activity and that the fibers are readily self-oxidized in the atmosphere.

When examined by X-ray analysis, a small portion of the fibrous metal copper prepared by the method just described consists of monocrystals, but the major portion of the fibers contains steps, kinks and curls.

The progress of growth of fibrous metals can generally be explained by the theory of dislocation. However, as the dislocation reaches the crystal surfaces steps or kinks are formed on the surfaces. As the formation of these steps and kinks is related to the growth of the crystals, it is presumed that such crystals manifest different characteristics than normal crystals. Further, since the dislocation itself causes formation or disappearance of point defects it is supposed that the phenomenon of dislocation is closely related to the catalytic action. For this reason, it may be considered that the point defects contribute to the catalytic action of the metal oxide catalysts.

Among metal oxide catalysts this invention contemplates the use of copper oxides having a great many number of point defects in treating CO and HC contained in the motor car exhaust gas.

The fibrous copper oxide catalyst of this invention is prepared by heating a mixture of copper oxide, metal halide and carbonaceous substance described above in a non-oxidizing atmosphere in a covered container. Such a catalyst can not be used for practical application when used singly for oxidizing harmful compounds contained in the motor car exhaust gas, because it has atendency of clogging, deformation, melting by heat and falling-off caused by the vibration during the running of the motor car.

Accordingly, to carry out the method of this invention,

following conditions should be fulfilled. The melting point of cuprous oxide (Cu O) is 1235 C., whereas that of cupric oxide (CuO) is 1326 C. For this reason, it is necessary to reinforce the copper oxides with heat resistant metal fibers having an excellent air permeability and a higher melting point than copper oxides because when these oxides are used as the catalyst, they are locally overheated and melted due to the presence of HC. It is necessary to use the fibrous copper oxide catalyst together with flexible web or the like made of fine wires of heat resistant alloys, such as SUS 24, 27, 32, 33 and 42 (AISI 430, 304, 316, 316L, 310$) stainless steels consisting of the base of iron and at least one of metals having a catalytic action, such as nickel and chromium, in view of their ready availability and favorable properties.

It was found that only when the above described fibrous catalyst prepared from the mixture of copper oxide, metal halide and carbonaceous substance is overlayed upon this web of the heat resistant metal fibers and hence reinforced and rendered heat resistant, the metal oxide fibrous catalyst can be used for treating the motor car exhaust gas under severe conditions. With a catalyst when using singly in the form of fibers or flakes, where the gas being treated contains a large amount of hydrocarbons, undesirable phenomena, such as melting, gas blowing and falling off of the catalyst element are noted. However this type of catalyst, when it is combined with the heat resistant web, is free from the above-mentioned defects.

According to the modified embodiment of this invention, the catalyst consists of a mixture of fine metal fibers containing one or both of copper and nickel, and graphite partially covered by copper or nickel or by oxide of copper or nickel formed by oxidizing the surfaces of these metals.

Said metal-coated graphite can be prepared by heat treating a mixture of metal oxide, metal halide and carbonaceous substance in a non-oxidizing atmosphere at a temperature at which said metals precipitate by reduction. The most preferable catalyst, that is the metalcoated graphite, can be obtained by using natural graphite in the form of relatively large flakes and by increasing the ratio of the carbonaceous substance to the metal oxide in carrying out the above described method.

The configuration and size of the metal-coated graphite may be such dimensions as ranging from 0.5 to 5 mm. It the size of graphite is smaller than 0.5 mm., the catalyst may be lost by being swept away by the stream of the exhaust gas, resulting in the loss of catalytic activity. On the other hand, if the dimension exceeds 5 mm., the surface area per unit weight becomes too small so that the catalytic reactor becomes too big for practical purposes.

To obtain metal-coated graphite of a desired dimension, it is advantageous to preliminarily mix the raw material mixture with a suitable amount of a heat resistant separator, for example, iron oxide, titanium oxide, aluminum oxide or silica in the form of fine powder.

The catalyst of this invention consisting of a mixture of fibrous metal and metal-coated graphite is prepared by heating the above described mixture of copper oxide, metal halide and carbonaceous substance in a non-oxidizing atmosphere. However, if the catalyst so produced is used in that condition for rendering the harmful compounds contained in the motor car exhaust gas harmless, there will arise such troubles as clogging, deformation, melting by heating and falling off caused by the vibration which occurs during the running of the motor car. For this reason, it is essential to use the catalyst together with the web mentioned above.

Following examples are given to explain the advantages of the novel fibrous copper oxide catalyst reinforced by a heat resistant metal web.

Example 1 An air laid web having a weight of 8 oz./yard was prepared by using a cold drawn wire of SUS 27 stainless 4 steel (Ni8%, Crl8%) having a diameter of 12 microns.

The web was used to form a bed having a width of 15 cm. and a length of 30 cm. A mixture consisting of 500 g. of oupric oxide (CuO), 25 g. of cuprous chloride (CuCl) and 50 g. of graphite was applied onto the bed to form a layer of the mixture having a uniform thickness. (In this case, the raw material mixture is held by the web and does not pass through.) Then the assembly was covered by a web of the weight of 8 oz./yard and the resulting assembly was put in a container with a lid and treated in a non-oxidizing furnace for two hours at a temperature of 750 C. While flowing nitrogen gas (N therein. Then the container was removed from the furnace and cooled gradually in a non-oxidizing atmosphere.

The fibrous copper held by the web was taken out from the container and loaded in the exhaust system (a mufller, for example) of an internal combustion engine and the air heated to 400 C. was passed through the fibrous copper for 30 minutes to convert the same into an oxide clad fibrous copper.

Exhaust gas of the composition consisting of 5% of CO, a small amount of O and the balance of N heated to 400 C. was passed through the catalyst layer at a rate of 300 to 400 liters per minute. The following table shows the percentage of CO gas removed through the above process.

TABLE 1 Type of gas CO Before passing through the catalyst percent 5.0 After passing through the catalyst do 0.1 Percentage of removal 98.0

Example 2 Several sheets of fine screen of mesh made of a cold drawn wire of SUS 27 (Ni-18%, Crl8%) were used as a bed and reinforcing materials for sandwiching the raw material mixture as hereinafter defined.

A mixture consisting of 500 g. of CuO, 20 g. of nickel chloride (NiCl 10 g. of CuCl and 50 g. of graphite was treated at a temperature of 780 C. for two hours to produce fibrous metallic copper. The resulting fibrous copper containing nickel was oxidized at a temperature of 500 C. for obtaining a fibrous copper oxide catalyst. Again, the catalyst was loaded in a mufller in the exhaust system of an internal combustion engine and a gaseous mixture heated to a temperature of 500 C. and consisting of 5% of CO, 1% of CH 8% of O and the balance of N was passed through the catalyst layer and obtained a percentage of CO removal as shown in Table 2.

TABLE 2 Type of gas CO Before passing through the catalyst percent 5.0 After passing through the catalyst do 0.1 Percentage of removal 98.0

When the temperature of the catalyst and the gas passed therethrough was raised beyond 600 C., it was possible not only to remove CO but also methane (CH in the exhaust gas at a percentage of removal of 97%.

Example 3 An air laid web having a weight of 8 oz./yard and made of a cold drawn wire of SUS 27 (Ni8%, Crl8%) having a diameter of 12 microns was used to form a bed having a width of 15 cm. and a length of 30 cm. A raw material mixture consisting of 500 g. of CuO, 25 g. of CuCl, 40 g. of the graphite flakes, 30 g. of graphite fine powder was applied onto the bed to form a layer of a uniform thickness. (In this case, the raw material mixture is held by the web and does not pass therethrough.) Then a web having a weight of 8 oz./yard was placed on the raw material layer. The resulting assembly was put in a container with a lid and treated at a temperature of 750 C. for two hours in a non-oxidizing furnace while flowing N gas. The heated assembly was taken out from the furnace and then cooled gradually in a non-oxidizing atmosphere.

The fibrous copper and copper-graphite composite body which are held by the web were taken out of the container and then loaded in a mufiler of the exhaust system of an internal combustion engine.

Exhaust gas of the composition consisting of 5% of CO, 3000 p.p.m. of NO lead compounds, 4% of O and the balance of N and heated to 600 C. was passed through the catalyst layer at a rate of 300-400 liters per minute and obtained percentages of removal as shown in Table 3.

A random web made of a cold drawn wire of SUS 32 having a diameter of 25 microns was used to form a bed. A mixture consisting of 500 g. of CuO, 20 g. of NiCl g. of CuCl and 70 g. of graphite (40 g. of graphite flakes and 30 g. of graphite powder) was placed on a bed and treated at a temperature of 780 C. for two hours to form a catalyst mixture consisting of fibrous copper and graphite particles coated by Ni-containing copper and the resulting catalyst was loaded in a muffler of the exhaust system of an internal combustion engine in the same manner as in Example 1. An exhaust gas heated to a temperature of 700 C. and consisting of 5% of CO, 3000 p.p.m. of NO lead compounds and the balance of N was passed through the catalyst layer and obtained percentages of removal as shown in the following Table 4.

When the temperature of the catalyst and the exhaust gas passed therethrough was raised beyond 800 C., it was possible to remove not only CO but also CA, in the exhaust gas.

[Example 5 An air laid web having a weight of 8 oz./yard and made of a cold drawn wire of SUS 27 (Ni-8%, Cr-l8%) having a diameter of 12 microns was used to form a bed having width of 15 cm. and a length of 30cm. and a raw material mixture consisting of 500* g. of Cu(), 25 g. of CuCl, 40 g. of graphite flakes, and 30 g. ofgraphite fine powder was applied onto the bed to form a layer of the mixture having a uniform thickness. (In this case also the raw material mixture is held by the web and does not pass therethrough.) Thereafter a web having a Weight of 8 oz./yard was placed on the layer of the raw material and the resulting assembly was put in a container provided with a'lid and treated at a temperature of 750 C. for one hour in a non-oxidizing furnace while flowing N Thereafter the heat treated assembly was taken out of the furnace and cooled gradually in a non-oxidizing atmosphere.

The fibrous copper and the copper-graphite composite body which are held by the web were removed from the container and loaded in a mufller in the exhaust system of an internal combustion engine. Then the air heated to a temperature of 400 C. was passed through the fibrous copper to convert the same into an oxide clad fibrous copper.

An exhaust gas consisting of 5% .of CO, 300 p.p.m. of CH 4% of O and the balance of N and heated to a 6 temperature of 500 C. was passed through the catalyst layer at a rate of 300 to 400 liters per minute and obtained percentages of removal of CO and CH as shown in the following Table 5.

TABLE 5 TABLE 5 Before passing through the catalyst 5.0% CH 300 p.p.m.

After passing through the catalyst 0.05% p.p.m.

Percentage of removal Type of gas Example 6 An air laid web made of a cold drawn Wire of SUS 32 having a diameter of 25 microns was used to form a bed, and a raw material mixture consisting of 500 g. of CuO, 20 g. of NiCl 10 g. of 01101 and 70 g. of graphite (40 g. of graphite flakes, and 30 g. of graphite fine powder) was applied onto the bed to form a raw material layer of a uniform thickness. The resulting assembly was treated at a temperature of 780 C. for two hours to produce fibrous copper containing nickel and graphite particles coated with Ni-containing copper which were oxidized at a temperature of 500 C. to obtain an oxidized catalyst. The catalyst was then loaded in a muffler in the same manner as in Example 1 and a gaseous mixture consisting of 5% of CO, 1% of CH 8%; of O and the balance of N and heated to 500 C. was passed through the mufller and obtained following percentages of removal of CO and CH TABLE 6 Before passing through the catalyst, percent Percentage of removal Type of gas CO CH The catalysts described in the foregoing examples do not deform, fall oif or melt. Moreover, they can pass the exhaust gas with an extremely small pressure loss. They are more effective than prior art catalysts wherein a fine powder of copper oxide is coated on a carrier such as alumina or silica. In addition, they can attain their ob ject under a large space velocity.

A similar effect can be produced in the following manner. A fibrous copper oxide or copper oxide-graphite composite particles is/are prepared in advance and applied all over said heat resistant metallic web, which is then rolled up, so as to obtain a sufliciently large contact area with the exhaust gas.

While the invention has been described in terms of some preferred embodiments thereof it should be understood that many changes and modifications will be obvious to one skilled in the art without departing from the true spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A method of manufacturing a fibrous catalyst consisting of at least one member selected from the group consisting of copper oxide, nickel oxide and coppernickel oxide adapted to be loaded in the exhaust system of an internal combustion engine for oxidizing CO and/ or HC contained in the exhaust gas, said method comprising the steps of (a) preparing a web made of a fine wire of an iron base heat resistant alloy,

(b) applying a mixture consisting of: (i) at least one member selected from the group consisting of copper oxide and nickel oxide, (ii) at least one member selected from the group consisting of copper halide and nickel halide, and (iii) carbonaceous substance comprising graphite upon said web to form an assembly comprising said web and a layer of the mixture thereon having a uniform thickness,

(c) heat treating the resulting assembly in neutral or reducing atmosphere to form a composite body comprising a fibrous metal or fibrous metal alloy, said fibrous metal or fibrous metal alloy being copper, nickel or copper-nickel alloy and being firmly bonded to said web, and

(d) oxidizing the resulting composite body to obtain said fibrous metal oxide or fibrous metal alloy oxide.

2. A method of manufacturing a fibrous catalyst, according to claim 1, wherein said step (a) comprises the step of preparing a web from a fine wire of an iron base heat resistant Ni, Cr or Ni-Cr alloy.

3. A method of manufacturing a fibrous catalyst, according to claim 1, wherein the web made is an air laid web.

4. A method of manufacturing a fibrous catalyst, according to claim 1, wherein the web made is a fine screen.

5. A method of manufacturing a fibrous catalyst, according to claim 1, wherein the web made is a random web.

6. A method of manufacturing a fibrous catalyst, according to claim 1, wherein said step (b) comprises the step of applying a mixture consisting of (i) either one of said metal oxides being Cu oxide, Ni oxide or Ni-Cu oxide, (ii) either one of said metal halides being Cu halide, Ni halide or Ni-Cu halide, (iii) and said carbonaceous substance being graphite, to form an assembly having a layer of the mixture with a uniform thickness.

7. A method of manufacturing a fibrous catalyst, ac- COrding to claim 1, wherein said step (c) comprises the step of heat treating the resulting assembly in a non- 8 oxidizing atmosphere at from about 750 C. to about 780 C.

8. A method of manufacturing a fibrous catalyst, according to claim 1, wherein said step (c) comprises the step of heat treating the resulting assembly in a container with a lid in a non-oxidizing atmosphere.

9. A method of manufacturing a fibrous catalyst, according to claim 1, wherein said step (c) comprises the step of obtaining either one of fibrous Cu alloy, Ni alloy or Ni-Cu alloy by heat treatment.

10. A method of manufacturing a fibrous catalyst, according to claim 1, wherein fibrous metal or fibrous alloy and a graphite partially covered with said metal or alloy are obtained, said fibrous metal or alloy and graphite being firmly bonded to the web.

11. A method of manufacturing a fibrous catalyst, according to claim 1, wherein the oxidation in said step (d) is effected at a temperature of from about 400 C. to about 500 C.

References Cited UNITED STATES PATENTS 2,750,346 6/1956 Sherwood 252--477 R 3,446,607 5/1969 Volk et al 252-447 X 3,495,950 2/1970 Barber et al. 252-447 R 3,565,574 2/1971 Kearby et a1. 252477 R CARL F. DEES, Primary Examiner U.S. Cl. X.R. 

